(1) Field of the Invention
The present invention relates to an instrument for measuring living body components, which is inserted and kept in the blood vessel and can measure living body components with a high accuracy.
(2) Description of the Related Art
As means for measuring blood gas components such as the oxygen partial pressure, the carbon dioxide gas partial pressure, the pH value and the saturated oxygen concentration in blood, and components contained in blood, such as potassium, sodium, calcium, glucose, lactic acid and urea, a method is generally adopted in which blood is collected and the measurement is performed by using a living body component analyzer. However, this method has a problem in that every time it is desired to know the state of blood components, blood must be collected from a patient and analyzed and it is difficult to determine the state of the patient from moment to moment. In addition, it is impossible to determine real-time changes of the living body components in a continuous manner. Recently, the significance of a continuous measurement of living body components has been recognized and the demand for this continuous measurement has increased. As a means for satisfying this demand, there has been tried a method in which a sensor for measuring living body components is directly inserted into the blood vessel by using an indwelling needle, an indwelling catheter or the like and is kept in the blood vessel to continuously measure the living body components.
In the method in which the measurement is carried out in the state where the sensor is kept in the blood vessel, often the measured value is different from the value obtained by analyzing blood taken from the living body, and the measurement is not performed stably with good reliability. In this method, a solution of blood anticoagulant is supplied from the indwelling needle or indwelling catheter to prevent coagulation of the blood. If the amount of the blood anticoagulant is small, the adhesion of coagulation products of blood to the sensing portion of the sensor cannot be sufficiently prevented and this adhesion results in a reduction of the measurement accuracy. Moreover, coagulation of the blood in the blood vessel is dangerous to the patient. If the blood anticoagulant is administered in an amount sufficient to prevent this adhesion, often the patient is adversely influenced. Accordingly, it is difficult to maintain a good balance between the amount of the blood anticoagulant administered and the adhesion-preventing effect.